Bonding between semiconductor elements and semiconductor element-mounting supporting members has conventionally been accomplished using silver pastes, for the most part. However, the increasing sizes of semiconductor elements and decreasing sizes and higher performance of semiconductor packages in recent years have also led to demand for smaller and more minute supporting members to be used in them. It is becoming impossible to meet this demand with silver pastes, because of runover due to wetting spread, wire bonding defects caused by the gradient of the semiconductor element, difficulty of thickness control of the silver paste, and generation of voids in the silver paste. In recent years, therefore, film-like adhesives that can help meet the demand have come into use (see Patent documents 1 and 2, for example).
Such film-like adhesives are used in methods for producing semiconductor devices that employ short bar attachment systems or wafer back-side attachment systems. For production of a semiconductor device by a short bar attachment system, first a film-like adhesive reel is cut out into short bars by cutting or punching and then bonded to a supporting member, and semiconductor elements individuated by a dicing step are connected to the film-like adhesive-attached supporting member to fabricate a semiconductor element-attached supporting member. This is followed by a wire bond step, sealing step and the like to obtain a semiconductor device (see Patent document 3, for example). In short bar attachment systems, however, a special assembly apparatus is necessary to cut out the film-like adhesive and bond it to the supporting member, and therefore production cost has been higher than methods using silver paste.
For production of semiconductor devices by a wafer back-side attachment system, on the other hand, first one side of a film-like adhesive is attached onto the back side of a semiconductor wafer, and a dicing sheet is pasted onto the other side of the film-like adhesive. The semiconductor element is then individuated from the semiconductor wafer by dicing, and the individuated film-like adhesive-attached semiconductor elements are picked up and connected to the supporting member. A semiconductor device is then obtained through steps such as wire bond and sealing. A wafer back-side attachment system does not require a special assembly apparatus for cutting out of the film-like adhesive and bonding to the supporting member, and a conventional assembly apparatus for silver paste may be used either in its original form or with part of the apparatus modified by addition of a heating plate or the like. Wafer back-side attachment systems have therefore been of interest as methods whereby production cost can be relatively limited, among methods using film-like adhesives (see Patent document 4, for example).
In recent years, incidentally, advances have been made in terms of the multifunctionality of semiconductor elements, in addition to their size reduction and higher performance, and there has been a surge in the number of semiconductor devices comprising stacks of semiconductor elements. The trend is also toward reduced thicknesses of semiconductor devices. Semiconductor wafers therefore continue to be further reduced in thickness.
In order to simplify the assembly process as well, methods have been proposed that simplify the attachment process onto the wafer back side, by preparing an adhesive sheet having a dicing sheet attached onto one side of a film-like adhesive, i.e. a film integrally comprising a dicing sheet and a die bond film (this will hereinafter be referred to as “dicing/die bond integrated film”). Because such methods can simplify the process of attachment of the film onto the wafer back side, they can lower the risk of wafer cracking. The softening temperature of the dicing tape is usually no higher than 100° C. Even with the integrated film described above, therefore, a film-like adhesive must be able to attach at low temperatures of below 100° C., in consideration of the softening temperature of the dicing tape, and of inhibiting wafer warping, in addition to having the satisfactory process properties mentioned above.
Semiconductor devices fabricated using film-like adhesives must also have reliability, or in other words, heat resistance, humidity resistance, reflow resistance and the like. In order to ensure reflow resistance it is necessary to exhibit high bonding strength that can prevent peeling or destruction of the die bond layer at a reflow heating temperature of around 260° C. Thus, demand is increasing for film-like adhesives that can exhibit high degrees of both process properties including a low-temperature lamination property, and reliability for semiconductor devices, including reflow resistance.
When the supporting member is an organic substrate with wiring on the surface, it is important for the film-like adhesive to have a sufficient filling property (embedding property) at different wiring levels, in order to ensure moisture-proof reliability of the semiconductor device and interconnect insulating reliability.
Film adhesives comprising combinations of thermoplastic resins with relatively low Tg and thermosetting resins have hitherto been proposed, in order to achieve both low-temperature workability and heat resistance (see Patent document 5, for example).